1. Field of the Invention
The present invention relates to a combination battery having a plurality of power source elements or electric elements, to a battery system having a plurality of combination batteries, and to an electric element control apparatus. The present invention relates also to an inverter motor system in which a DC is converted into a polyphase AC in an inverter to drive a polyphase AC, in particular, to an inverter motor system having an electric element with an operating voltage different from that of a polyphase AC motor.
2. Description of the Related Art
Conventionally, combination batteries having a plurality of power source elements have been known. In conventional combination batteries, because it is difficult to ensure a larger unit output voltage for each power source element, a plurality of power source elements, each with a lower unit output voltage relative to a desired output voltage, are serially connected so that a desired output voltage can be ensured as a whole. An example of the above structure is disclosed in Japanese Patent Laid-open Publication No. Hei 7-322516.
In the above described art, however, because the power source elements are serially connected, when an output of any one of the connected plurality of power source elements drops due to functional deterioration or other reasons, an output voltage of the whole battery accordingly drops by an amount equivalent to the drop in output of that power source element. In addition, in systems where an operational voltage of an auxiliary of an battery system differs from an output voltage of the battery of the battery system, a separate DC/DC converter must be provided.
Also, an inverter motor system for driving an electric vehicle, as shown in FIG. 10, has conventionally been known as one type of inverter motor system as described above. This system 200, which drives a vehicle driving motor via an inverter using a high voltage source, comprises an auxiliary 252 and an auxiliary power source 252, the operating voltage of both of which differs from that of a polyphase AC motor 240. As the voltage required by the auxiliary is lower than a vehicle driving voltage, a voltage from a high voltage source 210 is once reduced in a DC/DC converter 230, to which an auxiliary power source and the auxiliary are connected. With such a structure, system volume and weight increase, as does power loss, because of the use of a DC/DC converter. In order for this system to be connected to a plurality of additional electric elements with different operating voltages, additional DC/DC converter or converters must be provided to the element with different operating voltage, resulting in a further increase of system volume, weight, and power loss.
A system enabling an auxiliary power source to be connected to a high voltage source without a DC/DC converter is disclosed in the form of an electric system for an electric vehicle in Japanese Patent Laid-open Publication No. Hei 11-178114. In the system disclosed in that publication, an auxiliary power source is connected between a motor neutral point, where ends of a plurality of windings of a motor are connected to one another, and a lower voltage side of a high voltage source. This system structure enables system volume and weight to be reduced through elimination of a DC/DC converter.
However, in this system, the operating voltage of the connected electric element or elements must remain within a constant range because an auxiliary power source, serving as an electric element, is simply connected to the motor neutral point. Therefore, it is difficult to improve operational efficiency of an electric element which varies its operating state, depending on the varying operating state. Moreover, connection of a plurality of electric elements with different operating voltages requires a DC/DC converter. That is, the system voltage and weight are increased, as is power loss.
The present invention has been conceived in view of the above. According to the present invention, there is provided an electric element control apparatus according to the present invention, comprises a charge-storage element; a neutral point selectively connected to either a higher voltage side or a lower voltage side of the charge-storage element via a selection switch; a plurality of electric elements connected between the neutral point and either the higher voltage side or the lower voltage side of the charge-storage element, each electric element generating, consuming, or storing electric power; and a selection switch control section for controlling switching of the selection switch to thereby control potential at the neutral point. The thus structured electric element control apparatus can control operation of a plurality of, or a plurality of types of electric elements through control of the potential at the neutral point. This makes it possible to simplify the structure of an apparatus compared to an apparatus wherein a control mechanism is provided for each electric element.
According to another aspect of the present invention, there is provided a battery system. The battery system comprises serially connected combination batteries. This structure enables reduction of an output voltage required to each combination battery included in the battery system, relative to the entire output voltage of the battery system, so that accuracy in controlling an output of each battery, and thus a battery system including the combination batteries, can be improved.
According to still another aspect of the present invention, there is provided a combination battery, comprising a charge-storage element; a plurality of power source units connected in parallel to the charge-storage element, each including a power source element for outputting electric power; and an open/close switch connected to the power source element, for controlling a current passing through the power source unit by switching itself; and an open/close switch control section for controlling switching of each open/close switch, wherein the combination battery outputs electric power stored in the charge-storage element. The combination battery outputs power stored in the charge-storage element. In addition, current to an electric element is controlled in a similar manner.
This structure can control input and output power for every power source element by controlling the open/close switch. Therefore, even when an output of, for example, one of the plurality of power source elements should drop, increasing outputs from the power source units excluding the one including the power source element with a dropped output can compensate the output loss due to the drop as a whole battery. That is, a battery output control can be achieved with improved accuracy.
In one aspect of the present invention, a combination battery may further preferably comprise a neutral point selectively connected to either a higher voltage side or a lower voltage side of the charge-storage element via a selection switch; and a selection switch control section for controlling switching of the selection switch. Preferably, the power source units are connected between the neutral point and either a higher voltage side or a lower voltage side of the charge-storage element. This structure enables easy and accurate controlling of a combination battery output through controlling of the potential at the neutral point.
In another aspect of the present invention, preferably, a combination battery may further comprise a pair of output terminals, one of which is connected to the neutral point and another is connected to either the higher voltage side or the lower voltage side of the charge-storage element. As the selection switch control section can control the potential at the neutral point to a desired value, as described above, the use of the neutral point as an output terminal allows use of the neutral point as a power source terminal for an external load.
In still another aspect of the present invention, a combination battery may further preferably comprise a load element connected between the neutral point and either the higher voltage side or the lower voltage side of the charge-storage element, for power consumption. As this structure enables control of a voltage applied to the load element, using the selection switch, there is no need to provide a separate voltage application mechanism and voltage control mechanism for each load element.
In yet another aspect of the present invention, the load element of a combination battery may preferably be a load element for driving the combination battery. A load element for a combination battery may include a load element necessary in driving or adjusting driving of the combination battery, e.g., for a combination battery in the form of a fuel battery, a hydrogen flow amount control pump, a methanol reforming heater, a cooling fan, and so on.
According to another aspect of the present invention, there is provided an inverter motor system comprising
a charge-storage element for supplying a direct current;
an inverter having a plurality of selection switches each selectively connected to either a higher voltage side or a lower voltage side of the charge-storage element, for converting the direct current from the charge-storage element into a polyphase alternating current; a polyphase AC motor driven by the polyphase alternating current generated in the inverter; an electric element connected between a motor neutral point and either the higher voltage side or the lower voltage side, each electric element generating, consuming, or storing electric power, the motor neutral point being a point where one ends of a plurality of windings of the polyphase AC motor are connected to one another; a selection switch control section for controlling switching of the plurality of selection switches of the inverter to thereby control a potential at the motor neutral point; an open/close switch for switching between connections of the electric element to the motor neutral point and to either the higher voltage side or the lower voltage side of the charge-storage element, wherein the selection switch control section controls the plurality of selection switches, and switching of the open/close switch. As this arrangement enables desirable control of a voltage or current to to an electric element, appropriate operation of the electric element and improved system operation are facilitated.
In another aspect of the present invention, preferably, the selection switch control section controls switching of the plurality of switches and/or variably controls a potential at the motor neutral point, according to operational state of the plurality of electric elements. This allows the electric elements to operate appropriately according to the operational state thereof, so that system operation efficiency can be improved.
In yet another aspect of the present invention, preferably, each electric element is provided connectable to the higher voltage side and the lower voltage side of the charge-storage element via the open/close switch; and the selection switch control section controls the open/close switch so as to connect the electric element to either the higher voltage side or the lower voltage side of the charge-storage element. This enables appropriate switching of a voltage to apply or a current to supply to the electric elements, so that system operation efficiency can be improved.
In still another aspect of the present invention, preferably, an inverter motor system may further comprise a plurality of backflow circuits for each holding and backflowing a current passing through its associated electric element. This arrangement can eliminate power loss, so that system operation efficiency can be improved.
In yet another aspect of the present invention, preferably, the selection switch control section controls each switch according to operational state of its associated electric element among the plurality of electric elements included. As this arrangement enables appropriate controlling of a plurality types of electric elements, system volume, weight, and power loss can be reduced due to reduction of the number of DC/DC converters. Moreover, as the system can handle operation of a various kinds of electric elements, the system can be used in a wider variety of applications.